Abstract: A theoretical constitutive model describing the stress-strain behavior of rock subjected to different confining pressures is presented. A bounding surface plastic model with hardening effects is proposed which includes the effect of temperature drop. The bounding surface is based on a mapping rule and the temperature effect on rock is controlled by Poisson’s ratio. Validation of the results against available experimental data is also presented. The relation of deviatoric stress and axial strain is illustrated at different temperatures to analyze the effect of temperature decrease in terms of stiffness of the material.
Abstract: Increasing population growth requires more sustainable development of energy. This non-contaminated energy has an inexhaustible energy source. One of the vital parameters in such structures is the choice of foundation type. Suction caissons are now used extensively worldwide for offshore wind turbine. Considering the presence of a number of offshore wind farms in earthquake areas, the study of the seismic behavior of suction caisson is necessary for better design. In this paper, the results obtained from three suction caisson models with different diameter (D) and skirt length (L) in saturated sand were compared with centrifuge test results. All models are analyzed using 3D finite element (FE) method taking account of elasto-plastic Mohr–Coulomb constitutive model for soil which is available in the ABAQUS library. The earthquake load applied to the base of models with a maximum acceleration of 0.65g. The results showed that numerical method is in relative good agreement with centrifuge results. The settlement and rotation of foundation decrease by increasing the skirt length and foundation diameter. The sand soil outside the caisson is prone to liquefaction due to its low confinement.
Abstract: In this paper, a one-dimensional (1d) Parallel Elasto-
Plastic Model (PEPM), able to simulate the uniaxial dynamic
behavior of seismic isolators having a continuously decreasing
tangent stiffness with increasing displacement, is presented. The
parallel modeling concept is applied to discretize the continuously
decreasing tangent stiffness function, thus allowing to simulate the
dynamic behavior of seismic isolation bearings by putting linear
elastic and nonlinear elastic-perfectly plastic elements in parallel. The
mathematical model has been validated by comparing the
experimental force-displacement hysteresis loops, obtained testing a
helical wire rope isolator and a recycled rubber-fiber reinforced
bearing, with those predicted numerically. Good agreement between
the simulated and experimental results shows that the proposed
model can be an effective numerical tool to predict the forcedisplacement
relationship of seismic isolators within relatively large
displacements. Compared to the widely used Bouc-Wen model, the
proposed one allows to avoid the numerical solution of a first order
ordinary nonlinear differential equation for each time step of a
nonlinear time history analysis, thus reducing the computation effort,
and requires the evaluation of only three model parameters from
experimental tests, namely the initial tangent stiffness, the asymptotic
tangent stiffness, and a parameter defining the transition from the
initial to the asymptotic tangent stiffness.
Abstract: The importance of fibre reinforced plastics continually
increases due to the excellent mechanical properties, low material
and manufacturing costs combined with significant weight reduction.
Today, components are usually designed and calculated numerically
by using finite element methods (FEM) to avoid expensive laboratory
tests. These programs are based on material models including
material specific deformation characteristics. In this research project,
material models for short glass fibre reinforced plastics are presented
to simulate the visco-elasto-plastic deformation behaviour. Prior
to modelling specimens of the material EMS Grivory HTV-5H1,
consisting of a Polyphthalamide matrix reinforced by 50wt.-% of
short glass fibres, are characterized experimentally in terms of
the highly time dependent deformation behaviour of the matrix
material. To minimize the experimental effort, the cyclic deformation
behaviour under tensile and compressive loading (R = −1) is
characterized by isothermal complex low cycle fatigue (CLCF)
tests. Combining cycles under two strain amplitudes and strain
rates within three orders of magnitude and relaxation intervals
into one experiment the visco-elastic deformation is characterized.
To identify visco-plastic deformation monotonous tensile tests
either displacement controlled or strain controlled (CERT) are
compared. All relevant modelling parameters for this complex
superposition of simultaneously varying mechanical loadings are
quantified by these experiments. Subsequently, two different material
models are compared with respect to their accuracy describing the
visco-elasto-plastic deformation behaviour. First, based on Chaboche
an extended 12 parameter model (EVP-KV2) is used to model cyclic
visco-elasto-plasticity at two time scales. The parameters of the
model including a total separation of elastic and plastic deformation
are obtained by computational optimization using an evolutionary
algorithm based on a fitness function called genetic algorithm.
Second, the 12 parameter visco-elasto-plastic material model by
Launay is used. In detail, the model contains a different type of a
flow function based on the definition of the visco-plastic deformation
as a part of the overall deformation. The accuracy of the models is
verified by corresponding experimental LCF testing.
Abstract: In this paper, a two-dimensional method is developed to simulate the fillet welds in a stiffened cylindrical shell, using finite element method. The stiffener material is aluminum 2519. The thermo-elasto-plastic analysis is used to analyze the thermo-mechanical behavior. Due to the high heat flux rate of the welding process, two uncouple thermal and mechanical analysis are carried out instead of performing a single couple thermo-mechanical simulation. In order to investigate the effects of the welding procedures, two different welding techniques are examined. The resulted residual stresses and distortions due to different welding procedures are obtained. Furthermore, this study employed the technique of element birth and death to simulate the weld filler variation with time in fillet welds. The obtained results are in good agreement with the published experimental and three-dimensional numerical simulation results. Therefore, the proposed 2D modeling technique can effectively give the corresponding results of 3D models. Furthermore, by inspection of the obtained residual hoop and transverse stresses and angular distortions, proper welding procedure is suggested.
Abstract: Superstructures like offshore platforms, tall buildings, transition towers, skyscrapers and bridges are normally designed to resist compression, uplift and lateral forces from wind waves, negative skin friction, ship impact and other applied loads. Better understanding and the precise simulation of the response of batter piles under the action of independent uplift loads is a vital topic and an area of active research in the field of geotechnical engineering. This paper investigates the use of finite element code (FEC) to examine the behaviour of model batter piles penetrated in dense sand, subjected to pull-out pressure by means of numerical modelling. The concept of the Winkler Model (beam on elastic foundation) has been used in which the interaction between the pile embedded depth and adjacent soil in the bearing zone is simulated by nonlinear p-y curves. The analysis was conducted on different pile slenderness ratios (lc⁄d) ranging from 7.5, 15.22 and 30 respectively. In addition, the optimum batter angle for a model steel pile penetrated in dense sand has been chosen to be 20° as this is the best angle for this simulation as demonstrated by other researcher published in literature. In this numerical analysis, the soil response is idealized as elasto-plastic and the model piles are described as elastic materials for the purpose of simulation. The results revealed that the applied loads affect the pullout pile capacity as well as the lateral pile response for dense sand together with varying shear strength parameters linked to the pile critical depth. Furthermore, the pile pull-out capacity increases with increasing the pile aspect ratios.
Abstract: In this paper, a probabilistic framework based on
Fokker-Planck-Kolmogorov (FPK) approach has been applied to
simulate triaxial cyclic constitutive behavior of uncertain soils. The
framework builds upon previous work of the writers, and it has
been extended for cyclic probabilistic simulation of triaxial undrained
behavior of soils. von Mises elastic-perfectly plastic material model is
considered. It is shown that by using probabilistic framework, some of
the most important aspects of soil behavior under cyclic loading can
be captured even with a simple elastic-perfectly plastic constitutive
model.
Abstract: In this work, the plastic behaviour of cold-rolled zinc
coated dual-phase steel sheets DP600 and DP800 grades is firstly
investigated with the help of uniaxial, hydraulic bulge and Forming
Limit Curve (FLC) tests. The uniaxial tensile tests were performed in
three angular orientations with respect to the rolling direction to
evaluate the strain-hardening and plastic anisotropy. True stressstrain
curves at large strains were determined from hydraulic bulge
testing and fitted to a work-hardening equation. The limit strains are
defined at both localized necking and fracture conditions according to
Nakajima’s hemispherical punch procedure. Also, an elasto-plastic
localization model is proposed in order to predict strain and stress
based forming limit curves. The investigated dual-phase sheets
showed a good formability in the biaxial stretching and drawing FLC
regions. For both DP600 and DP800 sheets, the corresponding
numerical predictions overestimated and underestimated the
experimental limit strains in the biaxial stretching and drawing FLC
regions, respectively. This can be attributed to the restricted failure
necking condition adopted in the numerical model, which is not
suitable to describe the tensile and shear fracture mechanisms in
advanced high strength steels under equibiaxial and biaxial stretching
conditions.
Abstract: In this paper, an analytical simplified method for
calculating elasto-plastic stresses strains of notched bodies subject to
non-proportional loading paths is discussed. The method was based
on the Neuber notch correction, which relates the incremental elastic
and elastic-plastic strain energy densities at the notch root and the
material constitutive relationship. The validity of the method was
presented by comparing computed results of the proposed model
against finite element numerical data of notched shaft. The
comparison showed that the model estimated notch-root elasto-plastic
stresses strains with good accuracy using linear-elastic stresses. The
prosed model provides more efficient and simple analysis method
preferable to expensive experimental component tests and more
complex and time consuming incremental non-linear FE analysis.
The model is particularly suitable to perform fatigue life and fatigue
damage estimates of notched components subjected to nonproportional
loading paths.
Abstract: Outrigger-braced wall systems are commonly used to provide high rise buildings with the required lateral stiffness for wind and earthquake resistance. The existence of outriggers adds to the stiffness and strength of walls as reported by several studies. The effects of different parameters on the elasto-plastic dynamic behavior of outrigger-braced wall systems to earthquakes are investigated in this study. Parameters investigated include outrigger stiffness, concrete strength, and reinforcement arrangement as the main design parameters in wall design. In addition to being significantly affect the wall behavior, such parameters may lead to the change of failure mode and the delay of crack propagation and consequently failure as the wall is excited by earthquakes. Bi-linear stress-strain relation for concrete with limited tensile strength and truss members with bi-linear stress-strain relation for reinforcement were used in the finite element analysis of the problem. The famous earthquake record, El-Centro, 1940 is used in the study. Emphasize was given to the lateral drift, normal stresses and crack pattern as behavior controlling determinants. Results indicated significant effect of the studied parameters such that stiffer outrigger, higher grade concrete and concentrating the reinforcement at wall edges enhance the behavior of the system. Concrete stresses and cracking behavior are too much enhanced while less drift improvements are observed.
Abstract: In this paper, the elasto-plastic and cyclic torsion of a shaft is studied using a finite element method. The Prager kinematic hardening theory of plasticity with the Ramberg and Osgood stress-strain equation is used to evaluate the cyclic loading behavior of the shaft under the torsional loading. The material of shaft is assumed to follow the non-linear strain hardening property based on the Prager model. The finite element method with C1 continuity is developed and used for solution of the governing equations of the problem. The successive substitution iterative method is used to calculate the distribution of stresses and plastic strains in the shaft due to cyclic loads. The shear stress, effective stress, residual stress and elastic and plastic shear strain distribution are presented in the numerical results.
Abstract: The orthogonal processes to shape the triangle steel plate into a equilateral vertical steel are examined by an incremental elasto-plastic finite-element method based on an updated Lagrangian formulation. The highly non-linear problems due to the geometric changes, the inelastic constitutive behavior and the boundary conditions varied with deformation are taken into account in an incremental manner. On the contact boundary, a modified Coulomb friction mode is specially considered. A weighting factor r-minimum is employed to limit the step size of loading increment to linear relation. In particular, selective reduced integration was adopted to formulate the stiffness matrix. The simulated geometries of verticality could clearly demonstrate the vertical processes until unloading. A series of experiments and simulations were performed to validate the formulation in the theory, leading to the development of the computer codes. The whole deformation history and the distribution of stress, strain and thickness during the forming process were obtained by carefully considering the moving boundary condition in the finite-element method. Therefore, this modeling can be used for judging whether a equilateral vertical steel can be shaped successfully. The present work may be expected to improve the understanding of the formation of the equilateral vertical steel.
Abstract: True stress-strain curve of railhead steel is required to
investigate the behaviour of railhead under wheel loading through elasto-plastic Finite Element (FE) analysis. To reduce the rate of wear, the railhead material is hardened through annealing and
quenching. The Australian standard rail sections are not fully hardened and hence suffer from non-uniform distribution of the
material property; usage of average properties in the FE modelling can potentially induce error in the predicted plastic strains. Coupons
obtained at varying depths of the railhead were, therefore, tested under axial tension and the strains were measured using strain gauges as well as an image analysis technique, known as the Particle Image Velocimetry (PIV). The head hardened steel exhibit existence of three distinct zones of yield strength; the yield strength as the ratio of the average yield strength provided in the standard (σyr=780MPa) and
the corresponding depth as the ratio of the head hardened zone along
the axis of symmetry are as follows: (1.17 σyr, 20%), (1.06 σyr, 20%-80%) and (0.71 σyr, > 80%). The stress-strain curves exhibit limited plastic zone with fracture occurring at strain less than 0.1.
Abstract: In this study, the hydrogen transport phenomenon was
numerically evaluated by using hydrogen-enhanced localized
plasticity (HELP) mechanisms. Two dominant governing equations,
namely, the hydrogen transport model and the elasto-plastic model,
were introduced. In addition, the implicitly formulated equations of
the governing equations were implemented into ABAQUS UMAT
user-defined subroutines. The simulation results were compared to
published results to validate the proposed method.
Abstract: The large and small-scale shaking table tests, which
was conducted for investigating damage evolution of piles inside
liquefied soil, are numerically simulated and experimental verified by the3D nonlinear finite element analysis. Damage evolution of
elasto-plastic circular steel piles and reinforced concrete (RC) one with cracking and yield of reinforcement are focused on, and the failure patterns and residual damages are captured by the proposed constitutive models. The superstructure excitation behind quay wall is
reproduced as well.
Abstract: This paper focuses on the Mega-Sub Controlled
Structure Systems (MSCSS) performances and characteristics
regarding the new control principle contained in MSCSS subjected to
strong earthquake excitations. The adopted control scheme consists of
modulated sub-structures where the control action is achieved by
viscous dampers and sub-structure own configuration. The
elastic-plastic time history analysis under severe earthquake excitation
is analyzed base on the Finite Element Analysis Method (FEAM), and
some comparison results are also given in this paper. The result shows
that the MSCSS systems can remarkably reduce vibrations effects
more than the mega-sub structure (MSS). The study illustrates that the
improved MSCSS presents good seismic resistance ability even at 1.2g
and can absorb seismic energy in the structure, thus imply that
structural members cross section can be reduce and achieve to good
economic characteristics. Furthermore, the elasto-plastic analysis
demonstrates that the MSCSS is accurate enough regarding
international building evaluation and design codes. This paper also
shows that the elasto-plastic dynamic analysis method is a reasonable
and reliable analysis method for structures subjected to strong
earthquake excitations and that the computed results are more precise.
Abstract: In this paper, transversal vibration of buried pipelines
during loading induced by underground explosions is analyzed. The
pipeline is modeled as an infinite beam on an elastic foundation, so
that soil-structure interaction is considered by means of transverse
linear springs along the pipeline. The pipeline behavior is assumed to
be ideal elasto-plastic which an ultimate strain value limits the plastic
behavior. The blast loading is considered as a point load, considering
the affected length at some point of the pipeline, in which the
magnitude decreases exponentially with time. A closed-form solution
for the quasi-static problem is carried out for both elastic and elasticperfect
plastic behaviors of pipe materials. At the end, a comparative
study on steel and polyethylene pipes with different sizes buried in
various soil conditions, affected by a predefined underground
explosion is conducted, in which effect of each parameter is
discussed.
Abstract: The hydro-mechanical model for unsaturated soils has
been presented based on the effective stress principle taking into
account effects of drying-wetting process. The elasto-plastic
constitutive equations for stress-strain relations of the soil skeleton
have been established. A plasticity model is modified from modified
Cam-Clay model. The hardening rule has been established by
considering the isotropic consolidation paths. The effect of dryingwetting
process is introduced through the ¤ç parameter. All model
coefficients are identified in terms of measurable parameters. The
simulations from the proposed model are compared with the
experimental results. The model calibration was performed to extract
the model parameter from the experimental results. Good agreement
between the results predicted using proposed model and the
experimental results was obtained.
Abstract: Based on Rayleigh beam theory, the sub-impacts of a
free-free beam struck horizontally by a round-nosed rigid mass is
simulated by the finite difference method and the impact-separation
conditions. In order to obtain the sub-impact force, a uniaxial
compression elastic-plastic contact model is employed to analyze the
local deformation field on contact zone. It is found that the horizontal
impact is a complicated process including the elastic plastic
sub-impacts in sequence. There are two sub-zones of sub-impact. In
addition, it found that the elastic energy of the free-free beam is more
suitable for the Poisson collision hypothesis to explain compression
and recovery processes.
Abstract: In this paper, a plane-strain orthotropic elasto-plastic
dynamic constitutive model is established, and with this constitutive
model, the thermal shock wave induced by intense pulsed X-ray
radiation in cylinder shell composite is simulated by the finite element
code, then the properties of thermal shock wave propagation are
discussed. The results show that the thermal shock wave exhibit
different shapes under the radiation of soft and hard X-ray, and while
the composite is radiated along different principal axes, great
differences exist in some aspects, such as attenuation of the peak stress
value, spallation and so on.